Computer channels are the arrangements used by some computers such as IBM and IBM clone computers to communicate with other computers, peripheral equipment such as storage devices, and input/output devices such as terminals and printers. One such set of channels is defined by a standard known as the FIPS 60 standard defined by the National Bureau of Standards and operates at speeds of 3, 4.5, and eventually 6 megabytes per second. In the past, such high speed channels have been connected to low speed data networks. However, with the introduction and standardization of broadband integrated services digital network (B-ISDN) facilities such as those defined by CCITT and the IEEE 802.6 standard for metropolitan area networks, it becomes possible to transmit data at data channel rates over a data network. The B-ISDN network is described in "Broadband Aspects of ISDN-T1S1 Technical Subcommittee", Document T1S1.1/88-333, published by American National Standards Institute (1988), and the 802.6 network is described in "Project 802-Local and Metropolitan Area Networks Proposed Standard", prepared by the IEEE 802.6 Working Group, Jun. 26, 1988. A channel addresses a maximum total of 256 subchannel addresses and each address terminates on a device or software subsystem in a host computer. Arrangements exist for interconnecting 8 or 16 host channels using a Multisystem Channel Communication Unit (MCCU). The subchannel addresses are distributed among the potential destinations in accordance with information stored in a read only memory, initialized all installation time, defined within the MCCU. Thus in a case of a MCCU serving 8 channels, each channel may communicate with any other channel or device over 32 different subchannel addresses. With the use of MCCU, each sending channel sends data on a particular address within a range of addresses dedicated to that sending channel. This address is converted in the MCCU to a corresponding address for addressing the desired channels and, in some cases, an associated device. A problem with this type of unit is that it can only be used for accessing other channels or devices within typically 400 feet of the MCCU. The channels are therefore limited to being within 800 feet of each other. The requirement to pass state information from each channel for every subchannel address to each interacting channel on a given subchannel address, sufficiently rapidly to minimize the occurrence of "glare", wherein two ends of a communication between subchannels both generate "read" or "write" commands simultaneously, with small effect on performance due to this overhead, restricts this distance in the prior art. The current limitations include an overall throughput limitation to the bandwidth of 2 or 4 busses within the MCCU, and a limit of only 2 or 4 simultaneous conversations are possible between the 8 or 16 interconnected channels.
Other disadvantages of the MCCU are that it is not user programmable, i.e., it is set up in the factory using firmware to define the particular configuration for which it is being used. The MCCU arrangement limits each connected channel to a single communication at any one time and further limits the entire system to two or four simultaneous communications because of the presence of a shared bus within the MCCU. A channel has the ability to send to multiple destinations simultaneously; however, since the MCCU is a non-buffered device, it does not allow the channel to transmit until a data path is available, so that multiple transfers from over the same physical path and a channel cannot take place in the prior art.
In another arrangement in the prior art for communicating over long distress, computer channels are interconnected over a 1.5 megabit/second digital carrier facility. This arrangement is limited in bandwidth to the bandwidth provided by the digital carrier and is limited to connecting only the two channels at the endpoints of the carrier facility. There is therefore no provision for switching data blocks concurrently to more than one other channel.
While such high speed computer channels can be used advantageously for communications between two computers, or computers to devices or, in some cases, to a small group of such devices, the availability of B-ISDN facilities makes it possible for computers to communicate with a large number of other computers over a broadband network at channel speeds. However, there are no arrangements in the prior art which permit such connection. Further, a great deal of computer software is written on the assumption that computer channels communicate directly with other computer channels. The "handshake" arrangement for establishing connections between computer channels assumes that another channel is connected.
A problem of the prior art therefore is that there are no economically attractive arrangements whereby computer channels can communicate at high speeds with a large number of other computers or devices.